Wu Youxun

Wu Youxun a Chinese experimental physicist of the twentieth century (1897-1977) who worked on the Compton effect and on the scattering of X-rays and who helped to establish research and education in modern physics in China.

Early Life and Education

Wu Youxun was born on 2 November 1897 in Pingxiang, in Jiangxi province. He grew up in a period of reform and upheaval, when the older examination system was giving way to modern schools, and he was educated in the new institutions that were being founded to teach science and Western learning.

He entered Nanjing Higher Normal School, where he studied physics under teachers who were themselves among the first generation of Chinese-trained scientists. He graduated and taught for several years, but his ambition was to pursue research, and in 1921 he travelled to the United States to continue his studies.

He enrolled at the University of Chicago, one of the leading centres of experimental physics, and worked in the laboratory of Arthur Compton, who had recently discovered the effect that bears his name. The association placed Wu at the heart of one of the most important developments in modern physics and gave him the training that shaped his career.

The Compton Effect and X-Ray Scattering

The Compton effect concerns the change in wavelength of X-rays when they are scattered by electrons, a result that could be explained only if light behaved as a stream of particles carrying momentum. The discovery was a decisive piece of evidence for the quantum theory of radiation, and it was disputed by physicists who doubted that light could be both wave and particle.

Working in Compton's laboratory, Wu Youxun carried out experiments on the scattering of X-rays by various substances and obtained results that confirmed the predicted shift in wavelength and settled the controversy in favour of the quantum interpretation. His careful measurements of the intensity and polarisation of the scattered radiation provided some of the strongest evidence for the new theory.

His work on the scattering of X-rays was published in leading journals and became a standard reference. It demonstrated the reality of the momentum carried by photons and confirmed the theory of the scattering process as Compton had described it, and it established Wu's reputation as a precise and ingenious experimenter.

Return to China and Academic Career

Wu Youxun returned to China in 1926 and took up a professorship at Tsinghua University, where he joined Ye Qisun in building the physics department. He taught courses on modern physics and on experimental techniques, and he supervised research students, several of whom went on to distinguished careers.

In the 1930s he moved to other institutions, serving as a professor and administrator at several universities and contributing to the growth of scientific education. He worked to secure equipment and to create laboratories, and he argued for the importance of basic research in a country preoccupied with more immediate problems.

During the war years he accompanied his institution into the interior, and he helped to sustain teaching and research under conditions of great privation. He trained a generation of physicists in the fundamentals of their subject and maintained the standards of the discipline through a period when many scientific institutions were disrupted.

Leadership and Service

After the founding of the People's Republic, Wu Youxun was appointed head of the physics department of the Chinese Academy of Sciences and was elected a founding member of the academy in 1955. He worked to rebuild research in the physical sciences and to organise the institutes that would carry it out.

He served on national committees for science and planning and took part in the formulation of policies for the development of research. He was concerned with the training of scientific manpower and with the establishment of standards of academic quality, and he helped to organise the editing of scientific publications.

He also took part in the early discussions of the nuclear programme and lent his knowledge and standing to the effort. His experience of international physics and his administrative skill made him valuable in the translation of national aims into concrete programmes, though his own research career was largely concluded by the time the weapons programme began.

Influence and Legacy

Wu Youxun is remembered for his contributions to the understanding of the Compton effect, for which he received wide recognition, and for his role in founding physics education in China. His experiments on X-ray scattering are cited in the history of quantum theory as part of the evidence that established the particle nature of light.

He was a member of the Chinese Academy of Sciences and received national honours for his scientific work. The students he trained carried his standards into the research institutions and universities of the country, and his papers on scattering remain part of the record of the development of modern physics.

He died on 30 November 1977 in Beijing. His career joined the international physics of the 1920s with the building of Chinese science in the decades that followed, and he is honoured as an experimenter who contributed to a fundamental debate while helping to create the institutions of his native country.

See also

• Compton scattering
• Ye Qisun
• Arthur Compton
• Chinese Academy of Sciences